Following the success of USS Monitor – the ground-breaking ironclad warship, designed by Swedish-born engineer John Ericsson, that played a central role in the US Civil War Battle of Hampton Roads on 9 March 1862 – the US Navy issued a requirement for similar shallow-draft ironclads capable of operating in coastal waters and along the Mississippi River and its tributaries. Ericsson designed the new Casco-class vessels, which were deliberately kept as simple as possible to allow construction by small shipyards in as few as 40 days. Orders for a total of 20 were placed in early 1863 at the then-unprecedented total cost of $8m (roughly equivalent to $163m today).
However, the initial plans were heavily amended by the navy’s new ‘monitor office’, run by Chief Engineer Alban Stimers. As originally designed, the class had a draft of six feet, but Stimers arbitrarily reduced this to four feet, and increased the armour protection.
A rapid succession of further ‘improvements’ eroded the original simplicity of the design. Internal ballast tanks were added so that the vessel could take on water to lower its silhouette before going into action. These required elaborate pumping equipment, which added more weight, reducing the freeboard from 15 inches (380mm) to just 3 inches (76mm). This change was the final straw for Ericsson, who promptly resigned from the project.
